We study the role of the dipolar-induced resonance (DIR) in a quasi-one-dimensional system of ultracold bosons. We first describe the effect of the DIR on two particles in a harmonic trap. Then, we consider a deep optical lattice loaded with ultracold dipolar bosons. In order to describe this system, we introduce a novel atom-dimer extended Bose-Hubbard model, which is the minimal model correctly accounting for the DIR. We analyze the impact of the DIR on the phase diagram at $T=0$ by exact diagonalization of a small-sized system. We show that the DIR strongly affects this phase diagram. In particular, we predict the mass density wave to occur in a narrow domain corresponding to weak nearest-neighbor interactions, and we predict the occurrence of a collapse phase for stronger dipolar interactions.

We investigated the whispering gallery modes (WGMs) of cavities with a hexagonal cross section. We found two different modes, namely, perturbed and quasi-WGMs, of which the former exhibits a $Q$ of greater than ${10}^7$ when the corner radii are large and $1.8\times {10}^4$ when the corners are sharp. We studied the dependence of $Q$ on the curvature radius of the polygonal cavities and found that the coupling between the two modes determines the $Q$ of the cavity.

We report an experimental study on the intensity fluctuation-fluctuation correlations of chaotic-thermal light. This experiment introduced a detection protocol, which distinguishes positive and negative intensity fluctuations and lead to an intensity fluctuation-fluctuation correlation with 100% contrast from jointly measured photodetection events. This type of correlation provides a solution to achieve high visibility in thermal light ghost imaging. This study also explored other potential applications in which the higher-order coherence is necessary to be distinguished from the coexisting lower-order effects. In addition to its obvious importance in practical applications, this experiment brings us a broader vision in understanding the physical relationship between locally measured intensity fluctuations and the distant fluctuation-fluctuation correlations of chaotic-thermal light.

We analyze the dynamic optomechanical backaction in signal-recycled Michelson and Michelson-Sagnac interferometers that are operated off the dark port. We show that in this case—and in contrast to the well-studied canonical form of dynamic backaction on the dark port—optical damping in a Michelson-Sagnac interferometer acquires a nonzero value on cavity resonance, and additional stability and instability regions on either side of the resonance, revealing additional regimes of cooling and heating of micromechanical oscillators. In a free-mass Michelson interferometer for a certain region of parameters we predict a stable single-carrier optical spring (positive spring and positive damping), which can be utilized for the reduction of quantum noise in future-generation gravitational-wave detectors.

Rresonancelike enhancement of groups of adjacent peaks in the photoelectron spectrum of high-order above-threshold ionization has been well documented for noble-gas atoms subjected to intense infrared laser pulses. However, its physical origin is still under debate. In this Rapid Communication, we investigate experimentally and theoretically high-order above-threshold ionization of diatomic nitrogen and oxygen molecules in order to shed more light on the underlying mechanism. The resonancelike enhancement is experimentally observed for N${}_2$ but is absent for O${}_2$ molecules. A simulation on the basis of $S$-matrix theory and the strong-field approximation reproduces the experimental observations. This implies that the resonancelike enhancement can be attributed to the channel-closing effect. The specific molecular structure plays a decisive role for the presence or absence of this enhancement in molecular systems.

Complete positivity is a ubiquitous assumption in the study of quantum systems interacting with the environment. It will be shown that Hamiltonian evolution of a quantum system and its environment can be negative (i.e., not completely positive) in the energy basis, by showing that such evolution is almost always negative for given initial conditions. As such, ignoring or “correcting” experimental data that is not completely positive may cause the loss of important information regarding system-environment correlations and coupling. Complete positivity assumptions are an important part of many quantum information theories and it is important to understand how (and why) it appears to be possible to violate the complete positivity requirement in the examples presented here. A relationship between the negativity of an evolution and the eigenvalues of the Hamiltonian will be shown and experimental verification of negative reduced dynamics will be proposed.

We present a class of entanglement identifiers which has the following experimentally friendly feature: once the expectation value of the identifier exceeds some definite limit, we can conclude the state is entangled, even if not all measurements defining the identifier have been performed. These identifiers are in the form of sums of non-negative functions of correlations in a quantum state, mostly squares of correlations, and we illustrate their use and strengths on various examples.

Relative positions of twenty $n=28$ Rydberg levels of Th${}^{2+}$ with $L=9$, 10, 11, and 12 were determined with sub-MHz precision using the rf-RESIS (resonant excitation Stark ionization spectroscopy) technique. The pattern of binding energies was analyzed with the effective potential model, modified to account for significant nonadiabatic effects. The analysis yielded measurements of several properties of the Fr-like Th${}^{3+}$ core ion, including the quadrupole moment, $Q=0.5931$(14) a.u.; hexadecapole moment, Π $=$ −0.69(28) a.u.; $g$ factor, $g_J=1.24$(48); scalar and tensor dipole polarizabilities, α${}_D$${}_{,0}=15.224$(33) a.u. and α${}_D$${}_{,2}$ $=$ −5.30(11) a.u.; scalar quadrupole polarizability, α${}_Q$${}_{,0}=60$(15) a.u.; and the reduced dipole and octupole matrix elements connecting the ground 5$f$ ${}^2$$F_{5/2}$ level with the low-lying 6$d$ ${}^2$$D_{3/2}$ level, $\left|{\langle }^2{F}_{5/2}\right|\left|{\mathrm{M}}^{\left[1\right]}\right|{|}^2{D}_{3/2}\rangle |=1.436\left(2\right)$ a.u. and $\left|{\langle }^2{F}_{5/2}\right|\left|{\mathrm{M}}^{\left[3\right]}\right|{|}^2{D}_{3/2}\rangle |=3.3\left(1.1\right)$ a.u. The measured properties are compared with theoretical predictions.

We present an approach to the quantum-defect theory theory using the Jost functions and Jost solutions as the main building blocks. An attractive feature of this approach is that it allows us to avoid use of the explicit form of the solutions of the radial Schrödinger equation for the Coulomb problem. We obtain a concise representation of the Jost function for the superposition of the Coulomb and short-range potentials, which distinctly separates terms analytic in $k^2$ and terms singular at $k=0$. This representation can be used to design simple and efficient procedures allowing us to determine scattering phase shifts from the information about the bound states.

We have produced sympathetically cooled barium monohalide ions Ba$X^{+}$ ($X=\text{F}$, Cl, Br) by reacting trapped, laser-cooled Ba${}^{+}$ ions with room-temperature gas-phase neutral halogen-containing molecules. Reaction rates for two of these (SF${}_6$ and CH${}_3$Cl) have been measured and were found to be in agreement with classical models. Ba$X^{+}$ ions are promising candidates for cooling to the rovibrational ground state, and our method presents a straightforward way to produce these polar molecular ions.

We investigate the influence of intense driving fields whose components exhibit orthogonal polarizations on high-order-harmonic spectra from aligned diatomic molecules. We derive a generalized two-center interference condition, which accounts for $s-p$ mixing and the orbital symmetry, within the strong-field and the single-active electron approximation. We show that the nonvanishing ellipticity introduces an effective dynamic shift in the angle for which the two-center interference maxima and minima occur, with regard to the existing condition for linearly polarized fields. This shift depends on the ratio between the field-dressed momentum components of the returning electron parallel and perpendicular to the major ellipticity axis along each possible orbit. Because of this dependence, we find that there will be a blurring in the two-center interference minima, and that increasing ellipticity leads to splitting in such patterns. These features are investigated in detail for ${\mathrm{H}}_2$ and ${\mathrm{Ar}}_2$ in a bichromatic field composed of two orthogonally polarized waves.

The nonsequential double ionization (NSDI) of Mg atoms is investigated in both linearly and circularly polarized laser fields with different kinds of potentials. The numerical results indicate that the “knee” structure still exists in circularly polarized laser fields in the 800-nm case with different potentials, which can be well explained by the corresponding momentum and position distribution of electrons. Moreover, the ionized electron energy of Mg atoms at the end of the pulse also shows that the behavior of rescattering electrons is different between linearly and circularly polarized cases. Besides, we also look into the angular distribution at the end of the pulse with different kind of potentials to illustrate the difference in the double-ionization mechanism between the linearly and circularly polarized cases.

We present a detailed theoretical study on the photoionization of one- and two-electron atoms subject to an external changing plasma environment based on the Debye-Hückel model. Specifically, by examining the migration of the bound excited states into the continuum in the presence of plasma, our investigation has led to resonancelike photoionization structures immediately above the ionization thresholds for H, H${}^{-}$, and He atoms. For He, unlike the usual Fano-Beutler resonances due to the configuration mixing between the doubly excited components and the single ionization channel with different ${\ell }_1{\ell }_2$ angular momenta combinations in the final-state wave function, these plasma-induced resonancelike structures result from the mixing of the quasibound and continuum components of the same ${\ell }_1{\ell }_2$ combination in the final-state function. With a number of specific examples, we show that the general features of these spectra could be linked directly to the overlap at small $r$ between the effective wave functions of the outgoing ionized electron and the atomic electron in its initial states.

We study the dynamics of spin-1 atoms in a periodic optical-lattice potential and an external magnetic field in a quantum quench scenario where we start from a superfluid ground state in a shallow lattice potential and suddenly raise the lattice depth. The time evolution of the nonequilibrium state shows collective collapse-and-revival oscillations of matter-wave coherence as well as oscillations in the spin populations. We show that the complex pattern of these two types of oscillations reveals details about the superfluid and magnetic properties of the initial many-body ground state. Furthermore, we show that the strengths of the spin-dependent and spin-independent atom-atom interactions can be deduced from the observations. The Hamiltonian that describes the physics of the final deep lattice not only contains two-body interactions but also effective multibody interactions, which arise due to virtual excitations to higher bands. We derive these effective spin-dependent three-body interaction parameters for spin-1 atoms and describe how spin mixing is affected. Spinor atoms are unique in the sense that multibody interactions are directly evident in the in situ number densities in addition to the momentum distributions. We treat both antiferromagnetic (e.g., ${}^{23}$Na) and ferromagnetic (e.g., ${}^{87}$Rb and ${}^{41}$K) condensates.

Mixed photonic crystals (PCs), the photonic equivalent of semiconductor alloys, are ideal for use in investigating various phenomena occurring in disordered photonic systems. In the present study we fabricated highly disordered two-dimensional PCs, using a wafer-bonded InAsP/InP multiple-quantum-well slab, and examined the resultant photonic resonant modes by determining the spectrally and spatially resolved emission properties. We observed that new localized photon modes formed in the disordered PCs, which are in good contrast to the spatially extended band-edge modes associated with PCs having translational symmetry. Computer simulations confirmed the existence of such localized photon modes in the disordered PC structure.

Storing light based on the effect of electromagnetically induced transparency (EIT) provides a coherent way to transfer wave functions between photons and matters. The storage device is promising for the application of quantum memory. An important figure of merit for optical memory is fidelity, which can be degraded by either a two-photon detuning or an axial magnetic field gradient in the EIT scheme. We systematically studied the phase of readout light pulses with the beat-note interferometer. The detuning induces a nonuniform phase variation during the pulse propagation and a uniform phase shift during the light storage; in addition, the field gradient induces a nonuniform phase variation during the storage. We further demonstrated that the phase measurement can be used to diagnose a two-photon detuning below 10 kHz (or 1/600 of the excited-state natural linewidth) and a magnetic field gradient as low as 2 mG/cm. The fidelity of the readout pulse from the EIT memory can be achieved to 0.94. Our work provides useful information for practical applications of EIT-based quantum memory and advances the knowledge of EIT-related research fields.

We demonstrate that the frequency conversion in the cascaded processes can be mapped uniquely to an associated three-wave mixing processes in adiabatic evolution. After solving the coupling wave equations of three-wave mixing processes, we immediately find the solutions of the corresponding cascaded coupled equations. Furthermore, we introduce a rather simple model, which displays the main features of the optical stimulated Raman adiabatic passage (STIRAP) but allows for analytic evaluation of all quantities. It performs two simultaneous three-wave mixing processes efficiently and without significant generation of an intermediate frequency. At last, we consider in detail the effects of the phase mismatch to the optical STIRAP efficiency, which show that the analytic bounds are seen to describe the transfer region very accurately.

Ground-state properties of a single impurity in a one-dimensional Fermi gas are investigated in uniform and trapped geometries. The energy of a trapped system is obtained (i) by generalizing the McGuire expression from a uniform to trapped system (ii) within the local density approximation (iii) using the perturbative approach in the case of a weakly interacting impurity and (iv) diffusion Monte Carlo method. We demonstrate that there is a closed formula based on the exact solution of the homogeneous case which provides a precise estimation for the energy of a trapped system even for a small number of fermions and arbitrary coupling constant of the impurity. Using this expression, we analyze energy contributions from kinetic, interaction, and potential components, as well as spatial properties such as the system size and the pair-correlation function. Finally, we calculate the frequency of the breathing mode. Our analysis is directly connected and applicable to the recent experiments in microtraps.

The observation that violating Bell inequalities with high probability is possible even when the local measurements are randomly chosen, as occurs when local measurements cannot be suitably calibrated or the parties do not share a common reference frame, has recently attracted much theoretical and experimental effort. Here we show that this observation is only valid when the overall detection efficiency is very high ($\eta \ge 0.90$), otherwise, even when using the highest detection efficiency of recent photonic Bell tests, the probability of demonstrating nonlocality is negligible (e.g., it is smaller than $0.02\%$ for $\eta =0.785$). Our results show that detection efficiency is a much more critical resource for real-world applications than it was previously thought.

We present a quantum-defect theory (QDT) for the $-1/r^4$ type of long-range potential, as a foundation for a systematic understanding of charge-neutral quantum systems such as ion-atom, ion-molecule, electron-atom, and positron-atom interactions. The theory incorporates both conceptual and mathematical advances since earlier formulations of the theory. It also includes more detailed discussions of the concept of resonance spectrum and its representations, universal properties in charge-neutral quantum systems, and a QDT description of scattering resonances that is applicable to any $-1/r^n$ potential with $n>2$.